Piston



Patented Jan. 7, 1930 JOHN FLAMMANG, F 'UNIVERSITY CITY, AND

' SOURI, ASSIGN ORS, BY MESNE ASSIGNMENTS,

PERCY L. BOWSER, OF ST. LOUIS, MIS- TO THE STERLING CORPORATION, OF

WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE rrsToN Application filed January 15, 1927. Serial No. 161,263.

This invention pertains to pistons and more particularly to trunk pistons, such as are used in internal combustion engines and the like.

In an engine 'of this type, it is desirable to have a piston which is as light as possible, consistent with the necessary strength and rigidity. Numerous attempts have been made to construct pistons of light material, such as aluminum alloys, but since such alloys have a much higher co-eiiicient of thermal expansion than cast iron, they tend to expand when heated at -a greater rate than the cylinder in which they work; consequently, such a piston, if constructed in the ordinary way,

15 will either bind in the cylinder when hot or will have too loose a fit when cold. Attempts have been made to overcome this difficulty by making the skirt of such a iston in such a form as to be capable of yie ding circumferentially so that it may be made large enough to have a proper iit in the c linder when cold and yet will be capable o yielding when hot and expanded so as to prevent binding.

made substantlally symmetrical or so as to have both faces constructed to yield. This construction provides a uniform yielding on both sides of the piston. As is well known,

however, one side of the piston is subjected to greater pressures than the other side on account of the fact that the explosion always takes place on the downstroke of the piston, and during this stroke the connecting rod or pitman works at an angle to the cylinder axis always on the same side thereof. This angularity of the pitman tends to crowd the piston against one side of the cylinder with a greater pressure than is experiencedon the other side during the u stroke. When the engine is running at a ii piston reciprocating rapidly, the succession of explosions causes these pressures to be a plied in rapid succession. The effect on the piston is equivalent to a rapid succession of hammer blows on that side against which the piston is crowded. These hammer blows have a peening action on the material of the piston, tending to deform the same slightly. Ankother noticeable eiect of this peening action Such yielding pistons have heretofore been .i

igh speedand theis that the material of the piston is compacted and loses its resiliency. Consequently, the spring of the piston skirt on that side is eventually lost after a more or less prolonged operation of the same.

One of the objects of this invention is to provide a piston of light material and constructed to have a yielding t in the cylinder and at the same time to avoid a loss of resiliency by the peening action described above.

Another object is to provide such a piston, in which the bearing'surface which carries the heavier pressure is substantially solid or uninterrupted, while the skirt isV otherwise formed to have a yielding fit in the cylinder.

Further objects will appear from the followlng description, taken in connection with the accompanying drawing, in which Figure 1 is a side view of a piston embodying this invention;

Figure 2 is a section on line 2 2 of Figure l;

Figure 3 is a longitudinal section on line 33 of Figure 1; and

Figure 4 is a section on line 4-4 of Figure 3.

Referring to the drawing, 1 designates the head and 2 the skirt of the piston. The head is provided Awith the Yusual packing ring grooves 3 and the skirt with the usualwrist pin bosses 4. -Opposite the ends of the wrist pin bosses, the skirt is provided on each end with a relieved area 5 in which the surface of the skirt is undercut so as to relieve this portion of the skirt of contact with the cylinder wall.

One side of the skirtis cut so as to render the same resilient. A pair of longitudinal saw cuts 6 run from a point near the head to a point some distance short of the tipl of the skirt. These saw cuts are joined by a transverse saw cut- 7 about the middle of the p skirt. These saw cuts divide the skirt into sections rectangular in outline and extending 1n mutually opposed directions. Ihese sections extend longitudinally ofthe skirt and areeach hinged at one end to a comparatively rlgid portion of the skirt and are perfectly free for independent movement at their other ends. These sections are thus enabled to iex 10 Atom to within a short distance from the chamfer 10. This remaining portion of the skirt v is practically? solid, and is formed a few thousandths smaller to allow for expansion at thisA point.

The opposite side ofthe skirt-that is, the

side opposite the saw cuts 6 and 7-is left uncut, so that it will presenta solid bearing surface to the cylinder wall. This side of the piston is continuous so that there will be practically no yielding at any point between the bearing surface on that side and the wrist pin bosses. Accordingly, the side thrust of the pitman will come upon a rigid and unyielding portion of the piston skirt.

The lower end of the skirt is provided with a series of longitudinally extending saw cuts 8, which run from a short distance from the end of the skirt down to that end. This manner of cutting provides that the end or rim of the skirt shall also be resilient so as to insure a t of this part of the skirt in the cyl'- inder atall temperatures. The uncut side of the skirt does not have a saw cut 8, but is left continuous.

On both the solid bearing side and the cut or resilient side ofthe skirt, oil grooves 9 are cut. These grooves extend substantially the entire length of the skirt, but are not axial in their direction but make a slight angle with the direction of the axis. Accordingly, these grooves extend overa substantial portion of the circumference so that therel will be no tendency to wear the cylinder wall unevenly. The saw cuts 8 may also be canted at a similar angle for the same reason.

The upper edge of the skirtmay be chamfered, as shown at 10, so as to avoid a scraping edge, which will collect oil on the upstroke.

This edge of the skirt may also be provided with drain holes 11, communicating with the interior of the skirt, so that any oil collected at this edge will be drained to the interior and not pumped up past the packing rings. The last packing groove may also be provided with extended drain openings 12 so as to drain out anyj oil which may collect in this groove. This assists in preventing uthe oil from working past the upper packing rings and getting mto the combustion chamber. Each of the oil grooves 9 communicates not only with the drain hole 11 but also with the saw cut 7, which itself-has a tendency to collect oil. Consequently, there will not onlyv be a continual supply of oil maintained in the grooves 9, but an excess of oil therein may be avoided by draining through the holes 11. The area 5, which has some tendency to collect oil, may also be drainedto the interior of the piston by means of holes 13, communicating therewith.

It will be seen that this invention provides a piston which may be constructed of light material, having a high thermal expansion. It is so constructed that it may have a snug fit in the cylinder at all temperatures, its skirt" being resilient and capable ofyielding. in accordance with the temperature, and at the same time it presents a solid bearing surface to take the side thrust of the pit man. The side' of the piston which takes this thrust is solid and uncut, so that there will be no yielding whatever, and, consequently, no variation or loss of power in the action of the pitman. This side being originally constructed so as to be non-yielding, the etliciency of the piston and its iit in the cylinder is, therefore, not subject to deteriorat-ion on account of the peening -action or pounding of the piston in the cylinder. The cut side of the skirt provides ample resiliency to maintain a good iit, and this resiliency is provided at a point on the piston skirt which is not subject to excessive pounding or peening action. Consequently, the life and resiliency of this portion of the skirt is not subjectto deterioration. Accordingly, a piston of this construction will have a better action anda longer life than one of ordinary construction.

It is obvious that various changes may be made in the details of construction without departing from the spirit of this invention; it is to be understood, therefore, that this invention is not limitedto the specific details shown and described. 4

Having thus described the invention, what is claimed is:

1. A trunk piston for internal combustion one side of said bosses only to provide a pair of rectangular sections, each connected at one end to said skirt and free for independent movement at the other ends, said sections extendin from their connected ends longitudinally of the piston toward and opposite each other, said free ends being ared, and the opposite side of said skirt being uncut., e

3. A trunk piston for internal combustion engines', comprising, a head, and a skirt having -wrist-pin bosses, said skirt being cut on one side of said bosses only to provide a pair of rectangular sections, each connected at one end to said skirt andV free for independent movement at the othr end, said sections extending from their connected ends longitudinally of the piston toward and opposite each other, the opposite side of said skirt being uncut, and both bearing faces of said skirt having oil grooves therealong.

4. A trunk piston for internal combustion ,I engines, comprising, a head, and a skirt having Wrist-pin bosses, said skirt being cut on one side of said bosses only to provide a pair of rectangular sections, each connected at one end to said skirt andfree for independent movement at the other ends, said' longitudinally of the piston toward and op- I 

